The present invention relates to seals, and in particular to a seal for use on a shaft of a circulating fan in a paint cure oven.
Modem automobile and truck body protective coatings are applied as the body passes through a series of coating dip and spray booths and ovens. Coatings are set or initially cured in ovens that include the radiant heat type. Radiant heat ovens have a conveyor that runs the length of the oven to allow the bodies to move from one end of the oven to the other. Radiant heating is achieved by burning natural gas in an interior plenum to the oven. The inner oven side surfaces along the length of conveyor are heated by natural gas. This heated surface then radiates heat toward the body to be cured as it travels along on the conveyor.
The oven can be composed of one or more zones (up to 7 is common), each of which can be temperature controlled. Zone heating is used to ensure the quality of the coating. Circulating fans are used to prevent stratification of the heated air in the oven. If stratification were to occur, it could cause variations in the coating cure, which would produce a product of unacceptable quality due to over-cured coatings on upper portions of a vehicle body (hotter) and under-cured coatings on lower portions and in recessed areas of a vehicle body (cooler). Efficient oven operation is obtained with continuous and extended operation, which increases the need for ease of maintenance. Oven temperatures can range from ambient to over 350xc2x0 F.
The circulating fan includes a shaft-mounted impeller, which is driven by an electric motor using V-belts and sheaves. The shaft position is maintained by roller bearings, with the motor, belts, sheaves and bearings all supported on a common frame which is secured to the top of the oven. The fan impeller and part of the fan shaft extend vertically through the top of the oven, with the fan shaft passing through a pipe that is secured to, and extends above, the top of the oven. The outer shell of the oven is insulated for thermal efficiency and to prevent damage to various parts.
The pipe through which the fan shaft enters the oven acts as a chimney, drawing hot air from inside the oven and directing it upwardly where the hot air contacts the bearings, drying out the lubricant in the bearings and leading to premature failure. Also, any dirt flying around the shaft area, such as wear pieces from the V-belt drive, may fall through the clearance gap between the shaft and the pipe and into the oven area, possibly contaminating the finish on the pieces being cured inside the oven.
The present invention proposes the use of a split-boot seal which clamps around the shaft and caps off the pipe through which the shaft extends, substantially reducing the release of heat from the oven.
The seal of the present invention also redirects the flow of heated air which does escape from the oven via the pipe so that the heated air is no longer directed onto the bearings, thus further increasing the life of the bearings on the fan drive.
The seal of the present invention is of a two-piece design so it may be readily replaced from outside of the curing oven simply by releasing a clamp, removing the old seal halves, installing new seal halves, and reinstalling the clamp. This seal replacement takes minutes to complete, compared with the hours required to replace a traditional seal which involves entering the confined space of the main oven cavity to disassemble the shaft (and consequently the need to cool down the oven completely before any replacement work can be started).
The ease with which the seal of the present invention may be replaced, the fact that this seal substantially reduces the escape of heated air from the oven, and the fact that the heated air which does escape is effectively directed, by the seal, away from the bearings, results in cooler running bearings and permits the use of standard, off-the-shelf bearings instead of special, high temperature bearings for this application.
The seal of the present invention is secured to the fan shaft using a clamp and is located directly above the pipe passing through the oven. There is a gap between the seal and the top of the oven such that the seal does not contact any stationary oven part when the fan is in operation.